The invention disclosed and claimed herein generally pertains to a device for detachably coupling a source of electric power to a superconducting magnet. More particularly, the invention pertains to a device of such type which is designed to reduce resistance in establishing an electrical path between the source and an input lead of the magnet.
As is well known, a magnet can be made superconductive by placing it in an extremely cold environment, such as by enclosing it in a cryostat containing liquid helium or other cryogen. The extreme cold causes the resistance in the magnet coils to become negligible. A power source is initially connected to the coils, to introduce a current thereinto, and then removed. However, the current continues to flow through the coils due to the negligible resistance, thereby maintaining a magnetic field. Superconducting magnets find wide application, for example, in the field of magnetic resonance imaging.
In some common configurations, the magnet input terminals comprise lead pins located deep within the cryostat, proximate to the cryogen. Elongated connectors, coupled through cables to a power source, are inserted through ports to engage respective pins in electrically conductive relationship. After a current sufficient to establish a desired magnetic field has been coupled to the coils, the power leads are retracted through the ports.
In such arrangements, the contact surface or interface between a connector and a lead pin can have unacceptably high resistance to current flow, due to the temperature differential between the pin, located in the cryostat, and the connector which is initially at ambient temperature. If the resistance is too high, heat will be generated at the interface, causing the resistance to increase further, and possibly resulting in quenching of the magnet, i.e., loss of superconductivity. Resistance at the interface or contact surface is on the order of 50-100 micro-ohms for certain prior-art connectors.
In addition, prior art connectors of the above type have tended to use a spring-type mechanism which fits over the pin to hold the connector in place. Such mechanisms tend to have insufficient strength to tightly grip the pin, thereby also increasing resistance at the pin-connector interface. Such mechanisms may also be subject to frequent breakage.